[v2] doc: update atomic operation deprecation
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Commit Message
Update the incorrect description about atomic operations
with provided wrappers in deprecation doc[1].
[1]https://mails.dpdk.org/archives/dev/2021-July/213333.html
Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations semantics")
Cc: stable@dpdk.org
Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
---
doc/guides/rel_notes/deprecation.rst | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
Comments
23/07/2021 11:49, Joyce Kong:
> Update the incorrect description about atomic operations
> with provided wrappers in deprecation doc[1].
>
> [1]https://mails.dpdk.org/archives/dev/2021-July/213333.html
>
> Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations semantics")
> Cc: stable@dpdk.org
>
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Applied, thanks.
Considering all the questions regarding usage of atomics,
I still think we need a documentation about their correct use.
> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Saturday, July 31, 2021 3:27 PM
> To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; Joyce Kong <Joyce.Kong@arm.com>
> Cc: stephen@networkplumber.org; mdr@ashroe.eu; dev@dpdk.org; nd
> <nd@arm.com>; stable@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] doc: update atomic operation deprecation
>
> 23/07/2021 11:49, Joyce Kong:
> > Update the incorrect description about atomic operations with provided
> > wrappers in deprecation doc[1].
> >
> > [1]https://mails.dpdk.org/archives/dev/2021-July/213333.html
> >
> > Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations
> > semantics")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
>
> Applied, thanks.
>
> Considering all the questions regarding usage of atomics, I still think we need a
> documentation about their correct use.
I think few things to document are:
1) Use of __atomic_add_fetch vs __atomic_fetch_add
2) Using __ATOMIC_RELAXED for statistics
3) Using rte_atomic_thread_fence API
Anything else?
>
02/08/2021 19:22, Honnappa Nagarahalli:
> From: Thomas Monjalon <thomas@monjalon.net>
> > 23/07/2021 11:49, Joyce Kong:
> > Considering all the questions regarding usage of atomics, I still think we need a
> > documentation about their correct use.
>
> I think few things to document are:
> 1) Use of __atomic_add_fetch vs __atomic_fetch_add
> 2) Using __ATOMIC_RELAXED for statistics
> 3) Using rte_atomic_thread_fence API
That's a good list.
Let's start with that please.
I would like an explanation about when full barrier may be used.
@@ -19,16 +19,18 @@ Deprecation Notices
* rte_atomicNN_xxx: These APIs do not take memory order parameter. This does
not allow for writing optimized code for all the CPU architectures supported
- in DPDK. DPDK will adopt C11 atomic operations semantics and provide wrappers
- using C11 atomic built-ins. These wrappers must be used for patches that
- need to be merged in 20.08 onwards. This change will not introduce any
- performance degradation.
+ in DPDK. DPDK has adopted the atomic operations from
+ https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html. These
+ operations must be used for patches that need to be merged in 20.08 onwards.
+ This change will not introduce any performance degradation.
* rte_smp_*mb: These APIs provide full barrier functionality. However, many
- use cases do not require full barriers. To support such use cases, DPDK will
- adopt C11 barrier semantics and provide wrappers using C11 atomic built-ins.
- These wrappers must be used for patches that need to be merged in 20.08
- onwards. This change will not introduce any performance degradation.
+ use cases do not require full barriers. To support such use cases, DPDK has
+ adopted atomic operations from
+ https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html. These
+ operations and a new wrapper ``rte_atomic_thread_fence`` instead of
+ ``__atomic_thread_fence`` must be used for patches that need to be merged in
+ 20.08 onwards. This change will not introduce any performance degradation.
* lib: will fix extending some enum/define breaking the ABI. There are multiple
samples in DPDK that enum/define terminated with a ``.*MAX.*`` value which is